1. Field of the Invention
The present invention relates to novel methods and apparatus for recycling metal sheet-thermoplastic resin laminate composites such as ALPOLIC.
2. Discussion of the Background
Various composite laminates are known wherein a metal sheet is laminated on a thermoplastic synthetic resin sheet. U.S. Pat. No. 4,508,425 discloses a mirror manufactured by plating chromium on one surface of a metal sheet bonded to a composite sheet, made up of a synthetic resin sheet and the metal sheet, to form a mirror surface. The mirror may be worked to a desired shape and may be formed with a decorative pattern.
U.S. Pat. No. 4,560,623 discloses a specular product of bronze-like tone particularly suitable for use as a decorative material. The specular product uses, as a substrate, a composite board comprising a synthetic resin sheet and metal sheets laminated thereon, and includes a nickel deposit plated on the metal sheet and a specular film of Sn--Ni alloy electroplated on the nickel deposit using a specific electroplating bath.
U.S. Pat. No. 5,366,803 discloses metal-resin laminate composites in which the exterior surface of the metal sheet is coated with a layer of a cured polyvinylidene fluoride paint which is, in turn, coated with a layer of a cured fluorinated ethylene vinyl ether paint. These metal-resin laminate composites exhibit excellent weathering properties, may have a gloss of 25 to 80%, and may be bent to a sharp angle without cracking of the coating.
Such metal resin composites may have a structure in which a metal sheet is laminated to one surface of a thermoplastic resin sheet or, alternatively, a structure in which a metal sheet is laminated to both the top and bottom surfaces of a thermoplastic resin sheet.
Such laminates are useful for a number of architectural applications, because the laminates combine light weight with high strength. These laminates may be used as finished surfaces for all or portions of the interior or exterior surfaces of a building.
Because of the relative expense of the materials (metal sheet(s), and thermoplastic resin) and the high cost of disposal, it is desirable to recycle both the metal of the metal sheet and the thermoplastic resin of such composite laminates. It is especially desirable to recycle the "scraps" formed when large preformed sheets of such laminate composites are cut to the size required for a particular installation.
When the metal sheet(s) are composed of aluminum, it is important to separate the aluminum sheet(s) from the thermoplastic resin prior to melting the thermoplastic resin, because melting aluminum-thermoplastic resin laminates themselves leads to conversion of the aluminum to aluminum oxides and a poor yield of recovered aluminum. It is known to separate aluminum-polyethylene laminate composites by means of a two-stage process, in which the laminate is first heated and then pressed between picking rolls. However, this method is not effective when the aluminum sheet is relatively thick (e.g., 0.5 mm) or is composed of less pure and less flexible aluminum.
Thus, there remains a need for a method of separating metal sheet-thermoplastic resin laminate composites into their component metal sheet(s) and thermoplastic resin sheet. There also remains a need for suitable apparatus to carry out such a method.